Compared with traditional long-carbon-chain fossil fuels, natural gas has high reserves, a higher energy density, and does not contain sulphur. Natural gas fuel can produce remarkably lower emissions. It produces the lowest level of CO2 in all hydrocarbon fuels. Compared to traditional fossil fuels, natural gas reduces benzene emissions by 97%, NOx emissions by 80%, carbon monoxide (CO) emissions by 76%, and CO2 emissions by 22%. The use of nature gas does not produce lead, sulphur emissions, or particulate matters. When natural gas is cooled to a temperature of approximately −162° C. at atmospheric pressure, it condenses into liquefied natural gas (LNG). Since the density of LNG is 460 kg/m3, the volume of LNG takes up approximately 1/600 that of natural gas. LNG is an odourless, colourless, non-corrosive, and non-toxic liquid. The unit volume reduction dramatically eases its transport. The liquefaction process of natural gas removes O2, CO2, SOx, and water vapor. In addition, the lower fuel cost per unit mass of LNG becomes less in comparison with the traditional fossil fuels; LNG, mainly made up of paraffinic compounds, results in the combustion efficiency higher than that of traditional fossil fuels. Therefore, LNG is a promising fuel in the market of power generation.
Although LNG is convenient to transport and store with a specific volume compared with the gas phase, it is necessary to regasify LNG before combustion can take place in a gas turbine for stationary power generation. A large amount of cold energy can be produced during the regasification process while exhaust gas from combustion of regasified LNG in the gas turbine contains abundant low-temperature thermal energy.
Various LNG regasification systems have been disclosed, as well as systems to generate energy or power using the cold energy produced during LNG regasification. However, efficiency in regasification and power generation is still not optimized in any of the known systems, and can be further improved.